1. Field of the Invention
The present invention relates to a Broadband Wireless Access (BWA) system. More particularly, the present invention relates to an apparatus and method for selecting, releasing, and changing a MultiCast and BroadCast Service (MCBCS) channel of a Mobile Station (MS).
2. Description of the Related Art
In general, voice services have been a primary concern in the development of communication systems, and in addition to the voice services, providing various multimedia services as well as data services is becoming increasingly important when developing the communication systems. However, voice-based communication systems have failed to satisfy user demand due to a relatively small transmission bandwidth and expensive service fees. Moreover, advancing communication technologies and growing demand for Internet services have resulted in an increased need for a communication system capable of effectively providing the Internet services. To cope with such user demand, a Broadband Wireless Access (BWA) system has been introduced to effectively provide broadband Internet services.
In addition to voice services, the BWA system supports various data services with a high or low speed as well as multimedia application services (e.g., high-quality video). The BWA system is a wireless communication system that can access to a Public Switched Telephone Network (PSTN), a Public Switched Data Network (PSDN), an Internet network, an International Mobile Telecommunication (IMT) 2000 network, and an Asynchronous Transfer Mode (ATM) network in a fixed or mobile environment based on a wireless medium using a broadband spectrum (e.g., 2 GHz, 5 GHz, 26 GHz, 60 GHz, etc.). Furthermore, the BWA system can support a channel transmission rate of 2 Mbps or more. According to mobility of a user terminal (i.e., whether it is moving or fixed), a communication environment (i.e., indoor or outdoor), and a channel transmission rate, the BWA may be classified into a broadband wireless subscriber network, a broadband mobile access network, and a high-speed wireless Local Area Network (LAN).
A wireless access method of the BWA system is standardized by international standard organizations. One example of the BWA system is a Worldwide Interoperability for Microwave Access WiMAX system, which is standardized by an Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard group. According to the IEEE 802.16 standard, due to a wide bandwidth, large amounts of data can be transmitted at a short period of time in comparison with the conventional wireless technique for a voice service. In addition, a channel (or resource) can be shared by all users, resulting in the effective use of channel. Moreover, since a Quality of Service (QoS) is ensured, the users can receive different QoSs on the basis of service features.
IEEE 802.16 systems conform to a MultiCast and BroadCast Service (MCBCS, also referred to as MBS depending on standard group's or operator's intention) standard so as to provide multicast and broadcast services to a plurality of Mobile Stations (MSs). In the MCBCS standard, a Multicast and Broadcast Service_Zone (MBS_Zone) represents a zone including one sub-cell or a plurality of sub-cells for transmitting the same broadcast channels at the same time with the same frequency. Each sub-cell uses the same Connection IDentifier (CID) for the same broadcast channel or contents within the MBS_Zone. The sub-cell is a group including one frequency and one sector. In general, a Multicast CID (MCID) has a one-to-one mapping relation with one broadcast channel having a multicast Internet Protocol (IP). A Logical Channel ID (LCID) is mapped in one-to-one manner to a content ID, that is, an ID for identifying a plurality of broadcast contents included in a payload of the same multicast IP. A Base Station (BS) transmits an MBS_Zone ID list through a Downlink Channel Descriptor (DCD) message and broadcasts information indicating whether the BS is able to provide an MCBCS service and indicating a zone where the BS belongs. The MBS_Zone may be constructed of one BS or a plurality of BSs.
Unlike the conventional unicast service, the MCBCS simultaneously transmits the same broadcast contents to a plurality of BSs with the same frequency. Then, an MS combines and uses packets received from the BSs, thereby improving reception throughput. The conventional unicast service has a problem in that, when the MS is located at an edge of a cell, data is not smoothly transmitted and received due to significant interference between cells. However, in the case of MCBCS, even when the MS exists in the cell edge, it is possible to receive, combine, and use the same data from the plurality of BSs because a neighboring BS transmits the same contents at the same synchronized time. This effect is referred to as a macro diversity gain.
The MCBCS service can transmit broadcast contents by multicast or broadcast to all MSs existing within the MBS_Zone that provides a specific broadcast service. With the MCBCS service, not only a downlink unidirectional broadcast service but also an uplink bidirectional connection can be possible according to characteristics of the 802.16 system.
Various capacities for all flows of the MCBCS service are required, for example, 32 Kbps, 64 Kbps, 128 Kbps, 256 Kbps, 384 Kbps, 500 Kbps, 1 Mbps, etc. A capacity less than or equal to 64 Kbps is used when contents (e.g., audio, text message, etc.) are provided through the MCBCS service. Typical video & audio services used in a Digital Multimedia Broadcasting (DMB) require a capacity of 384 Kbps. A low-quality video service requires a capacity of 128 Kbps, and a high-quality video service requires a capacity of 1 Mbps or more. In general, in the case of the MCBCS service, a channel configuration and a transmission rate are different for each MBS_Zone.
Basically, user information is managed by a Subscription Profile Repository (SPR). When a security service is additionally provided, the SPR interacts with the security server to perform user authentication. Currently, there is a standard by which a policy server interacts with the SPR in order to obtain user information or to perform user authentication. However, there is no standard by which the policy server interacts with the security server.
In the current IEEE 802.16 standard, only a physical layer and a Media Access Control (MAC) layer are defined, and there is no method of selecting, releasing, and changing a channel. Therefore, in order to support an integrated service (i.e., MCBCS), a signaling process for dealing with a broadcast channel must be defined.